Suddenly, I can't use my key

My account has the right to access a repository.
I added a pub key to my account.
until few days ago, I have not problem to use it with the pub key.

but suddenly, I can't access the repo with the pub key.

== result when I do "git push" ==
git@bitbucket.org: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
== end ==

I'm work in linux env.
I want to use a specific priv key.
so I created a Host like this.
== my ssh/config ==
Host NEW_HOST
Hostname bitbucket.org
IdentityFile ~/.ssh/MY_PRIV_KEY.pem
== end ==

I already mentioned, I did NOT have any problem until few days ago.

so I tried to make new priv & new pub key.
and add the new pub key to bitbucket to my account.

I can push with the new priv key.
so I think BITBUCKET is blocking my priv key.

Folloing is my questions.

1. can you tell me what's wrong?
2. How can I figure out my key pairs are blocking or not.

thanks.